This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. At least five arenaviruses cause viral hemorrhagic fevers in humans. Lassa virus, an Old World arenavirus, utilizes the cellular receptor alpha-dystroglycan to infect cells1. Machupo, Guanarito, Junin, and Sabia viruses are New World hemorrhagic fever viruses that do not use alpha-dystroglycan2. Here we demonstrate a specific, high-affinity association between transferrin receptor 1 (TfR1) and the entry glycoprotein (GP) of Machupo virus. Expression of human TfR1, but not human transferrin receptor 2, in hamster cell lines markedly enhanced infection of viruses pseudotyped with the GP of Machupo and Junin viruses, but not Lassa or lymphocytic choriomeningitis viruses. An anti-TfR1 antibody efficiently inhibited replication of Machupo, Guanarito, Junin, and Sabia viruses, but not that of Lassa virus. Iron depletion of culture media enhanced, and iron supplementation reduced, the efficiency of infection by Junin and Machupo but not Lassa pseudoviruses.